Feature request: activity type or API to end Copilot loading state without rendering content

[EulerMacaroni]

Summary

When building agents with the Agents-for-js SDK that target Microsoft's hosted Copilot UI, there is no supported way to stop the built-in loading indicator without sending a visible message (as far I know). I'd like a first-party activity type (e.g., void) or adapter-side API that ends the turn and dismisses the spinner while keeping the conversation transcript unchanged.

Scenario

• For agent runs long-running work, and the final response comes asynchronous.
• Once work finishes, the agent has nothing further to show but wants the client to exit the "sync" / loading state so the experience feels asynchronous.
• Attempting to rely on deleteActivity after sending an interim message only clears the transcript after the Copilot UI is reloaded; the deletion is not reflected in real time.

Expected behavior

• The SDK (and Copilot UI integration) expose a supported signal/activity to indicate "no further reply, dismiss loading state".
• Alternatively, deleteActivity events propagate to the hosted Copilot client immediately.

Actual behavior

• All activities must carry user-visible text or cards to affect the UI; there's no way to send a "void" or equivalent activity.
• deleteActivity removes the transcript entry server-side, but the hosted Copilot UI only reflects the change after a refresh.

Impact

• Agents that need to return control to the user without extra text must fall back to empty messages or custom channels, which is confusing for users.
• Deleting corrective messages doesn't help because the UI doesn't update live.